Plasma etching operations are common in the manufacture of articles such as integrated circuits. The performance of the plasma etch operation is highly dependent on the density and uniformity of the plasma. In the past, optical emission methods have been used to monitor the density of the plasma. For example, the ratio of emissions from two different species has been used as an estimate of the relative abundance of ionic or excited species.
Typical optical emission spectroscopy measurements are made using light from a large volume of the plasma discharge. The measurement of the large volume thus represents an average concentration or integrated concentrations within the observed volume. Information concerning localized density or concentration measurements cannot be determined with such measurement techniques. U.S. Pat. No. 4,615,761 provides an example of a method and apparatus wherein a sample is only taken from a single location in the plasma.
In view of the deficiencies and disadvantages of the prior art plasma density measurement techniques, it would be desirable to provide an apparatus and method for acquiring spatially resolved density and concentration information concerning a plasma.
In accordance with one aspect of the invention, an apparatus for measuring plasma characteristics at various locations in a plasma in a plasma reaction chamber is provided. The apparatus includes a photosensitive detector, and a scanner that receives light emissions from different points in a volume of plasma in a plasma reaction chamber. The apparatus further includes a light directing element that directs light emissions from the volume scanned by the scanner to the photosensitive detector, the photosensitive detector generating signals corresponding to detected amounts of the light from the volume at the different points. The apparatus also includes a processor wherein the signals are analyzed and converted to data representative of characteristics of the plasma at the different points.
In accordance with another aspect of the present invention, a method for mapping characteristics at different locations in a volume of plasma in a plasma reaction chamber is disclosed. According to the method, a volume of plasma in a plasma reaction chamber is scanned to obtain light emission samples from different points in the volume of plasma. Light emissions from the scanned volume are directed to a photosensitive detector. One or more signals corresponding to amounts of light emissions detected by the photosensitive detector are generated. The signals are processed to estimate one or more characteristics of the plasma at the different points.